Gas-filled overvoltage arrester for telecommunication installations

ABSTRACT

1,109,332. Cold-cathode tubes. CERBERUS A.G. 17 March, 1966 [17 March, 1965], No. 11688/66. Heading H1D. A gas-filled overvoltage protector tube includes a pair of opposed planar electrodes each of which has rounded edges, a thickness of not less than 1 mm., and major faces each having an area not less than 30 (mm.)&lt;SP&gt;2&lt;/SP&gt;, the spacing between the electrodes, and their thermal capacity, being such as to ensure that, when the tube is loaded at 1000 watts with 10 amps r.m.s. current, a fusion bead forms at the surface of the electrodes to produce a shortcircuit prior to destruction of the hard glass envelope of the tube. Each electrode is preferably of nickel coated with calcium oxide and has a channel 3a, Fig. 1, in its rear face within which its lead-in wire 3 is staked (Fig. 3, not shown) and brazed. The filling is a mixture of argon, hydrogen and tritium at 80 torr. The tube has a polyethylene clip 12, Fig. 4, mounted on the exhaust tip end of the tube, two nickel channel members 10 extending along opposite sides of the tube, each having one end hooked in the clip and the other end spot-welded to the externally extending portion 7 of a respective lead-in pin, whereby the tube may be readily introduced into the contact spring fixture of a fuse-box.

United States Patent US. Cl. 313-210 10 Claims ABSTRACT OF THEDISCLOSURE A novel gas-filled overvoltage arrester is disclosed, theovervoltage arrester being characterized by the features thatplate-shaped electrodes retarding the fusion process are arranged in aglass body or bulb formed of hard glass, the plate-shaped electrodespossessing rounded edges and at least one millimeter thickness andhaving a surface area of thirty square millimeters. The plateshapedelectrodes are spaced from one another at a sufiiciently small distanceto render possible sudden shortcircuits due to the formation of a fusionbead at the surface of the electrodes, the thermocapacity of theelectrodes being so large that with a current load of ten or moreamperes R.M.S. and with more than 1,000 watts per second, the fusionbead positively forms prior to the destruction of the glass body.

The present invention relates to an improved gas-filled overvoltagearrester for protecting low-voltage telecommunication installations andis of the type incorporating two electrodes arranged in a glass bulb.The invention also pertains to an improved construction of electrodeassembly for the aforementioned gas-filled overvoltage arrester.

Gas-filled overvoltage arresters have been known to the art for morethan twenty years. However, they exhibit an insufficient overvoltageprotection because they respond too slowly to steep voltage surges.Attempts have been made to reduce ignition lags by the use ofradioactive additives or emitters. In so doing, it was still notpossible to eliminate the insufficient current load-carrying capacity.In actual practice, this disadvantage manifests itself in that uponexceeding a predetermined load-carrying capacity limit there appearcracks or complete destruction of the glass bulb occurs without theresimultaneously occurring a short-circuit at the electrodes. Due to theentry of atmospheric air into the glass bulb, the operating voltage ofthe overvoltage arrester considerably exceeded the normal rated value.As a result, further overvoltages are no longer removed so that thesesteep voltage surges resulted in the destruction of the object to beprotected. Even frequent control of the voltage arrester was not able toafford satisfactory security since an arrester which was destroyed by anovervoltage could not be readily perceived by merely visually inspectingsuch.

Overvoltage or voltage arresters have already become known to the artwhich exhibit a greater load-carrying capacity. Nonetheless, theirsecurity remains limited because even with overloading their operatingvoltage changes due to deformation of the electrodes or rupture of theglass housing, and without positively leading to a short-circuit. As aresult, the object to be protected is no longer protected from furtherovervoltages.

Accordingly, it is a primary object of the present invention to providean improved gas-filled overvoltage 3,450,923 Patented June 17, 1969arrester for telecommunication installations which overcomes theaforementioned disadvantages of the prior art devices.

A further, more specific object of this invention is an improvedconstruction of arrester which positively protects an object fromovervoltages and which possesses very high operational reliability.

Yet another very noteworthy object of this invention relates to theprovision of an improved voltage arrester which is relatively economicalto manufacture, has quite small dimensions yet still possesses a highload-carrying capacity, is extremely reliable in operation and thusrequires a minimum of maintenance, and also has a long operating life.

Still a further important object of this invention concerns itself withan improved electrode construction particularly suitable for use with anovervoltage arrester.

The inventive overvoltage or voltage arrester combines the features ofhigh load-carrying capacity and quick response time with thecharacteristic of instantaneously bringing about permanent short-circuitof the electrodes upon overload without any considerable change of theoperating voltage and before another type of destruction of the arrestercan occur. The installation to be protected is short-circuited and is,therefore, protected from further overvoltages. Due to the short-circuitwhich positively occurs in every instance of overload, the defectiveovervoltage arrester is immediately localized and can be exchanged bythe operating personnel.

Generally speaking, the inventive gas-filled overvoltage arrester ischaracterized by the features that, plate-shaped electrodes retardingthe fusion process are arranged in a glass body or bulb formed of hardglass, said plateshaped electrodes possessing rounded edges and at leastone millimeter thickness and having a surface area of thirty squaremillimeters. Moreover, according to the invention, such plate-shapedelectrodes are spaced from one another at a sutficiently small distanceto render possible sudden short-circuit due to the formation of a fusionhead at the surface of the electrodes, and wherein the thermal capacityof the electrodes is so large that with a current load of ten or moreamperes R.M.S. and with more than 1,000 watts per second the fusion beadpositively forms prior to the destruction of the glass body.

Other features, objects and advantages of the invention will becomeapparent by reference to the following detailed description and drawingsin which:

FIGURE 1 is a cross-sectional view of a preferred embodiment ofinventive arrester;

FIGURE 2 is a front view of the inventive arrester showing theconfronting arrangement of the two spaced electrodes;

FIGURE 3 is a side view of the arrester of FIGURE 2 depicting the mannerof connecting the lead-in pin with the associated electrode;

FIGURE 4 depicts the inventive arrester of FIGURES 1 to 3 as arranged inits socket;

FIGURE 5 is a side view of the arrangement of FIG- URE 4; and

FIGURE 6 is a top view of FIGURE 4.

Describing now the drawings and initially referring to FIGURES 1 to 3,it will be seen that the inventive arrester comprises a body'or bulb 1formed of hard glass and internally of which the tungsten lead-in wires3 of the lead-in pins 311 and which are presealed with a glass tube orhose 4 are fused to the glass body 1 by means of these glass tubes 4.The lead-in pins 3b incorporating the tungsten lead-in wires 3 and thetherewith connected externally projecting nickel free end portions 7carry the confronting and spaced substantially late-shaped electrodes 2and 2a. The glass tubes or hoses 4 which increase the insulating pathbetween the electrodes 2 and 2a can be seen in FIGURE 2 to projectinternally of the glass bulb 1 and are fused to its base portion 1a.Both of the electrodes 2 and 2a are advantageously formed of nickel andpossess a surface area of preferably 10 x 6 millimeters and a thicknessof 2.5 millimeters. They are connected with the tungsten lead-in wires 3or, for instance, one millimeter diameter, by mechanical wedging, asgenerally indicated by reference character 5, and are hard soldered orbrazed throughout the entire electrode length. Of course, otherdimensions for the electrodes are possible insofar as they result in anappropriately high thermal stability and heat capacity. It has beenfound that these plate-shaped electrodes 2 and 2a should preferablypossess a thickness of at least one millimeter with a surface area of atleast thirty square millimeters.

The cross-sectional showing of FIGURE 1 depicts the manner in which thetungsten lead-in wires 3 of the lead-in pins 3b are embedded in arespective channel 3a formed at the rear face of the associatedelectrodes 2 and 2a, whereby there is ensured for good electrical andthermal contact between these electrodes 2, 2a and the lead-in wires 3,and such electrodes during higher thermal loads with discharge arcs areadditionally reinforced. It is also possible to apply, in known manner,to the confronting faces of the plate-shaped electrodes 2 and 2a asuitable layer of material 6 favoring emission. As already developed,the outermost portion of free end 7 of the lead-in pins 3badvantageously consists of a nickel wire which can be satisfactorilyconnected by butt welding 8 with the associated tungsten lead-in wire 3.The fusion head which short-circuits the arrester upon the appearance ofan overload forms in the gap between the activated confronting faces ofthe electrodes 2 and 2a and, specifically, because of the advantageousinventive feature of rounding the edges 9 of these electrodes 2 and 2aat all sides, as shown, such bead generally appears in the middle of theelectrode surfaces.

According to a preferred embodiment of the invention there is employedfor the layer of material 6 favoring emission calcium carbonate. This istransformed in the usual manner into calcium oxide. It ensures for arapid transition of the gas discharge from the glow-discharge phase intothe arc phase already at approximately 200 milliamperes as well as aburning voltage which lies such that, by the direct-current voltageswhich are normally used in telecommunication networks, there occurs afaultless eXtinguishin-g of the arrester insofar as such has ignited,that is, the burning voltage lies above the normal supply voltage.

In FIGURES 4, and 6 there is shown an insulating clip or member 12formed of polyethylene and mounted at the pump tip bulb end 11 of theglass bulb 1. Hooked into this clip 12, or otherwise attached, are bothof the nickel contact rails extending along opposite lengthwise sides ofthe glass bulb 1. This insulation clip 12 thereby serves to fix orinterconnect these two contact rails 10 with one another and to alsoprotect the glass bulb 1. At the opposite bulb end, that is, the sideremote fromthe pump tip 11, these contact rails 10 are provided Withnickel contact bars 14. These nickel contact bars 14 are connected withthe externally extending portion 7 of each of the associated lead-inpins 312 by spot-weld- Ihe inventive arrester is advantageously filledwith a gas mixture consisting of argon, hydrogen and tritium, and with afilling pressure of 80 millimeters mercury pressure. The nickel contactrails 10 together with the clip 12 provide a socket for the arrester andat the same time protect the glass body or bulb 1 against mechanicalstress or loads. The arrester thus provided with its socket can beeffortlessly and easily introduced into the contact spring fixture ofthe fuse box. Additionally, this construction renders it easier toundertake any eventually required exchange or replacement of thearrester in the fuse boxes which normally contain a larger number ofsuch arresters.

While there is shown and described a present preferred embodiment of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and practicedwithin the scope of the following claims.

What is claimed is:

1. A gas-filled overvoltage arrester for telecommunication installationscomprising a bulb formed of hard glass, a pair of substantiallyplate-shaped electrodes arranged within said glass bulb, saidplate-shaped electrodes having rounded edges and each possessing atleast a thickness of one millimeter and a surface area of thirty squaremillimeters, said plate-shaped electrodes being spaced from one anotherat a relatively small distance sufficient to bring about a suddenshort-circuit due to the formation of a fusion bead at the surface ofsaid plate-shaped electrodes, said plate-shaped electrodes possessing aheat capacity which is sufficiently large so that with a current load ofat least ten amperes R.M.S. and with more than 1,000 watts per second,the fusion bead positively forms prior to the distruction of said glassbulb, said glass bulb possessing two oppositely situated lengthwiseextending sides, a contact rail arranged at each said lengthwiseextending side of said glass bulb, said glass bulb further possessing atone end a pump tip, lead-in pins connected to each electrode extendingout of said glass bulb at the side opposite to said pump tip, a clip forprotecting said pump .tip and for affixing said contact rails to saidglass bulb at the side of said pump tip, said contact rails being weldedat said opposite side to at least one of said lead-in pins.

2. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim 1, wherein said lead-in pins are formed ofhigh-melting metal and are connected with each plate-shaped electrode bymechanical wedging and brazing to thereby increase the strength of saidplateshaped electrodes with regard to deformation and at the same timeto provide satisfactory electrical and thermal contact between saidplate-shaped electrodes and their associated lead-in pins.

3. A gas-filled over-voltage arrester for telecommunicationinstallations as defined in claim 2, wherein said glass bulb is filledwith a gas filling primarily containing an inert gas with which there iscommingled a gaseous beta-emitter.

4. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim 3, wherein said gas filling with which said gasbulbis filled contains a mixture of argon, hydrogen and tritium andpossesses a filling pressure of about millimeters mercury pressure.

5. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim. 2, wherein said plateshaped electrodes are formedof nickel.

6. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim 2, wherein the surface of said plate-shapedelectrodes is covered with a layer of material favoring emission inorder to accelerate the transition of the gas discharge from the glowdischarge phase into the arc phase.

7. A gas-filled overvoltage arrester for telecommunicainstallations asdefined in claim 6, wherein said layer of material favoring emission isformed of calcium oxide.

8. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim 2, wherein the rear face of said plate-shapedelectrodes is provided with a channel in which there are seated andafiixed said lead-in pins.

9. A gas-filled overvoltage arrester for telecommunication installationsas defined in claim 2, wherein said plateshaped electrodes are formed ofnickel and said lead-in pins are at least partially formed of tungsten.

10. A gas-filled overvoltage arrester for telecommunica installations asdefined in claim 9', wherein said leadin pins also include a portionformed of nickel defining the free end thereof.

(References on following page) References Cited UNITED STATES PATENTSChapman 313352 X Stevenson 313325 X Holden 313-214 X Gray 313214 X Dobke313-214 X Herre 313-325 X 6 2,056,662 10/1936 Foulke 313-353 X 2,415,8162/1947 Depew et a1 313214 X 2,716,714 8/1955 Adams et a1. 313332 X JOHNW. HUCKERT, Primary Examiner, 5 A. J. JAMES, Assistant Examiner. US. 01.X.R. 317-62; 313-182, 325, 352

"M050 UNITED STATES PATENT OFFICE 569 CERTIFICATE OF CORRECTION PatentNo. 3,450,923 Dated June 11, 1969 Inventor(s) G- mm It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the specification, Column 1, line 28, "1,000 watts per second shouldread 1,000 watt-seconds Column 2, line 43, "1,000 watts per second"should read 1,000 watt-seconds --7 Column 4, line 21, "1,000 watts persecond" should read 1,000 watt-seconds SIGNED AND SEALED (SEAL) Attest:

Edward Fletcher 11 WILLIAM E scam I Attesting Officer Gonmissioner ofPatents

